There is a strong consensus among legal experts that EU law was and remains incorporated into UK law by virtue of an Act of Parliament. Doctrines such as the duty of consistent interpretation (the obligation of national courts to interpret national law, as far as possible, in conformity with EU legislation), the principle of direct effect (the capacity of a provision of EU law to produce cognisable legal effects within the national system) and the principle of supremacy (the preference given to EU law where national law is incompatible with directly effective EU provisions) all apply within the UK thanks to the Parliamentary mandate created by the European Communities Act 1972, as interpreted by the UK courts in landmark rulings such as R v Secretary of State for Transport, ex parte Factortame (No 2) [1990] 3 WLR 818 and R v Secretary of State for Employment, ex parte Equal Opportunities Commission [1995] 1 AC 1.

On the basis of that mandate, the UK courts will interpret UK legislation in conformity with our EU obligations and will disapply UK legislation if it conflicts with directly effective EU law. The requirement that directly effective EU law enjoys supremacy in the event of an irreconcilable conflict with national law is a highly significant practical reality within the UK—but it does not take effect in some autonomous manner, directly under the authority of the European Union or the European Court of Justice, independently of or despite the will of Parliament itself. Its fundamental constitutional basis remains the principle of Parliamentary sovereignty.
https://publications.parliament.uk/pa/cm201011/cmselect/cmeu...

the “duty of consistent interpretation” of national law with Community law
https://www.newlawjournal.co.uk/content/major-impact

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Note added at 3175 days (2017-10-29 22:55:49 GMT) Post-grading
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the duty to interpret national law in conformity with EU law